GB2032640A

GB2032640A - Liquid crystal display device

Info

Publication number: GB2032640A
Application number: GB7926419A
Authority: GB
Original assignee: Suwa Seikosha KK
Current assignee: Suwa Seikosha KK
Priority date: 1978-10-03
Filing date: 1979-07-30
Publication date: 1980-05-08
Also published as: CH642216B; JPS5548729A; US4376567A; JPS5825241B2; CH642216GA3; GB2032640B; HK4686A

Abstract

A liquid crystal display device comprises two electro-optic 90 DEG twist cells in tandem, between polarisers and with no interposed light affecting elements, the alignments in the upper cell U and lower cell L being one of the combinations 20-23, where the solid and dashed arrows respectively relate to the upper and lower surfaces of the liquid crystal layers, whereby the display exhibits maximum contrast when viewed from between the 4.30 and 7.30 directions. Both layers exhibit the same degree of contrast in the 6 o'clock direction, have the same twist sense and may be of the same material. When both layers are in the twisted state the polariser through which light is transmitted to cell U is arranged to provide a linear polarisation always at 90 DEG to the long liquid crystal axis, to reduce light absorption. The two layers may be arranged to display different types of information. <IMAGE>

Description

1 GB 2 032 640 A 1 SPECIFICAMON Liquid crystal display device This

invention relates to liquid crystal display devices, for example, for electronic timepieces such as watches.

According to the present invention there is provided a liquid crystal display device comprising: two liquid crystal layers each sandwiched between two transparent electrode substrates; and a pair of polarising plates between which the electrode substrate and liquid crystal layers are disposed, the arrangement being such that the long axes of the molecules of one of the liquid crystal layers adjacent one electrode substrate thereof are in the 9 o'clock - 3 o'clock or 3 o'clock - 9 o'clock direction, the long axes of the molecules of said one liquid crystal layer adjacent the other electrode substrate thereof are in the 6 o'clock - 12 o'clock or 12 o'clock - 6 o'clock range, the long axes of the molecules of the other liquid crystal layer adjacent one electrode substrate thereof are in the 12 o'clock - 6 o'clock or 6 o'clock - 12 o'clock direction, and the long axes of the molecules of the said other liquid crystal layer adjacent the other electrode substrate 90 thereof are in the 9 o'clock - 3 o'clock -or 3 o'clock - 9 o'clock direction, so that the direction of maximum contrast of said liquid crystal layers lies between the 4:30 and 7:30 directions.

In the preferred embodiment one of the 95 electrode substrates is in contact with both liquid crystal layers.

Preferably the liquid crystal layers are composed of the same liquid crystal material.

Ina preferred embodiment the long axes of the 100 molecules of the liquid crystal layers are aligned in a given direction by rubbin the surfaces of the respective electrode substrates.

The invention is illustrated, merely by way of example, in the accompanying drawings, in 105 which:

Figure 1 is a cross-sectional view of a liquid crystal display device of the type to which the present invention relates; Figure 2 is a schematic perspective view of one 110 embodiment of a liquid crystal display device according to the present invention; Figure 3 is a contrast distribution diagram of the liquid crystal display device of Figure 2; Figure 4 illustrates the various types of data displayed by the liquid crystal display device of Figure 2; and Figure 5 illustrates various other embodiments of liquid crystal display devices according to the present invention.

A liquid crystal display device of the type to which the present invention is shown in Figure 1 and comprises transparent electrode substrates 1, liquid crystal layers 2 and polarising plates 3. The liquid crystal layers 2 are of the twisted nernatic 125 type having a 900 twisted structure in the viewing direction.

The present invention seeks to reduce the light absorption of the liquid crystal layers 2, 3 by making the vibrating direction of the light penetrating the liquid crystal layers always perpendicular to the direction of the long axes of the liquid crystal molecules; seeks to make a liquid crystal display device of the type illustrated in Figure 1 easy to manufacture by utilizing the same liquid crystal material (including an additional material for controlling the twist direction if necessary) for the two liquid layers and by making the twist direction in the two liquid crystal layers the same; and seeks to remove non-uniformity of display contrast between the liquid crystal layers when the liquid crystal display device is viewed from the 6 o'clock direction.

Recently liquid crystal display devices have come to be used in various equipment. To increase the range of data displayed conventional liquid crystal display devices having two liquid layers as shown in Figure 1 have been developed. In such conventional liquid crystal display devices, the alignment of the liquid crystal molecules is not described in detail. In the following embodiments of the present invention, the alignment of the liquid crystal molecules in the two liquid crystal layers is the optimum and the external appearance of the liquid crystal display devices is good and furthermore manufacture of Hquid crystal material and ot the liquid crystal display device is facilitated.

Figure 2 illustates, in detail, an embodiment of a liquid crystal display device according to the ' present invention. This liquid crystal display device comprises transparent electrode plates 4a, 4b, 4c, an upper liquid crystal layer 5 sandwiched between the electrode plates 4a, 4b, a lower liquid crystal layer 6 sandwiched between the electrode plates 4b, 4c, a polarising plate 7a polarised in a direction indicated by arrow 8, and a polarising plate 7b polarised in a direction indicated by arrow 9. The electrode plate 4a is rubbed in a direction indicated by arrow 10, the surface of the electrode plate 4b facing the electrode plate 4a is rubbed in a direction indicated by arrow 11 and the surface of the electrode plate 4b facing the electrode plate 4c is rubbed in a direction indicated by arrow 12, and the electrode plate 4c is rubbed in a direction indicated by arrow 13. Reference numerals 14, 15, 16, 17 indicate the 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock directions respectively. In the lower liquid crystal layer 6, the long axes of the molecules adjacent the electrode plate 4b are aligned in the 6 o'clock 12 o'clock direction and the long axes of the molecules adjacen ' t the electrode plate 4c are aligned in the 9 o'clock 3 o'clock direction. Thus the lower liquid crystal layer 6 has a twisted structure (i.e. from the electrode plate 4c to the electrode plate 4b) from the 3 o'clock direction to the 6 o'clock direction.

The long axes of the molecules of the upper liquid crystal layer 5 adjacent the electrode plate 4b are aligned in the 12 o'clock - 6 o'clock direction and adjacent the electrode plate 4a are aligned in the 9 o'clock - 3 o'clock direction. Thus the upper liquid crystal layer 5 has a twisted structure (i.e. from the electrode plate 4b to the 2 GB 2 032 640 A 2 electrode plate 4a) from the 6 o'clock direction to the 9 o'clock direction. Accordingly, the upper and lower liquid crystal layers 5, 6 have together a clockwise twisted structure, and so it is not necessary to provide the upper liquid crystal layer 5 with a chemical additive for controlling the twist direction that is different from the chemical additive for controlling the twist direction of the lower liquid crystal layer 6. Thus if a hole is provided in both the electrode plate 4b and the electrode plate 4a, the two liquid crystal layers 5, 6 can be provided in a single operation, the hole in the electrode plate 4a subsequently being hermatically sealed. This is advantageous from the point'f view that the same liquid crystal material can be used for both the upper and lower liquid crystal layers and from the point of view of manufacture of the liquid crystal display device.

If the polarising direction of the polarising plates 7a, 7b are as shown in Figure 2, the vibrating 85 direction of the transmitted light is always perpendicular to the long axes of the respective liquid crystal molecules in the liquid crystal layers.

Accordingly, light absorption by the liquid crystal layers can be minimised and so a bright display can be obtained. The relationship between the direction of observation and the distribution of contrast for the liquid crystal display device of Figure 2 is shown in figure 3. The solid line shows the distribution of contrast in the case of display by the upper liquid crystal layer 5. The broken line. ' 95 shows the distribution of contrast by the lower liquid crystal layer 6. The best contrast in the upper liquid crystal layer can be obtained by viewing from the 7:30 direction indicated by arrow 18. The best contrast in the lower liquid 100 crystal layer can be obtained by viewing from the 4:30 direction indicated by arrow 19. When the liquid crystal display device is viewed from the 6 o'clock direction the contrast is the same in both the upper and lower liquid crystal layers. In this case, non-uniformity of display contrast in the upp(r and lower liquid crystal layers is eliminated.

Figure 4 shows the respective displays produced by the upper and lower liquid crystal layers. Figure 4 (a) shows a display of 11 H 32M 38S on Monday, February 27th. The numeral ---27---is displayed by the lower liquid crystal layer and the other numerals and letters are displayed by the upper liquid crystal layer. Figure 4(b) shows the case where the display is changed and the 115 calendar of February 197 8 is displayed. The numeral -2- is displayed by the upper liquid crystal layer and the other numerals and letters are displayed by the lower liquid crystal layer.

Figure 5 is a diagram showing the rubbing directions of the electrode plates in various embodiments of the present invention, column 20 being the embodiment already described in relation to Figure 2. Letters "U" and -L- refer to the upper and lower liquid crystal layers 5, 6 respectively. The broken lines indicate the rubbing directions on the surface of the electrode plates which are in contact with the liquid crystal molecules in the lower part of the relspective liquid crystal layers, i.e. the electrode plates 4b and 4c. The solid lines show the rubbing directions on the surfaces of the electrode plates which are in contact with the liquid crystal molecules in the upper part of the respective liquid crystal layers, i.e. the electrode plates 4a and 4b. Columns 21 to 23 in Figure 5 illustrate other embodiments of the present invention which are as advantageous as the embodiment indicated in column 20. Only liquid crystal display devices where the long axes of the liquid crystal molecules are aligned by rubbing is described above but the aligning may be achieved by angular deposition by adapting the depositing direction to achieve the same alignment as in the case of rubbing.

The embodiments of the present invention described above provide great advantages, namely, that the display contrast at the respective liquid crystal layers is the same when viewed from the 6 o'clock direction, that the same liquid crystal material may be used for both layers and that light absorption by the liquid crystal layers can be minimised.

Claims

1. A liquid crystal display device comprising:

two liquid crystal layers each sandwiched between two transparent electrode substrates; and a pair of polarising plates between which the electrode substrate and liquid crystal layers are disposed, the arrangement being such that the long axes of the molecules of one of the liquid crystal layers adjacent one electrode substrate thereof are in the 9 o'clock - 3 o'clock or 3 o'clock - 9 o'clock direction, the long axes of the molecules of said one liquid crystal layer adjacent the other electrode substrate thereof are in the 6 o'clock - 12 o'clock or 12 o'clock - 6 o'clock range, the long axes of the molecules of the other liquid crystal layer adjacent one electrode ' substrate thereof are in the 12 o'clock - 6 o'clock or 6 o'clock - 12 o'clock direction, and the long axes of the molecules of the said other liquid crystal layer adjacent the other electrode substrate thereof are in the 9 o'clock - 3 o'clock or 3 o'clock - 9 o'clock direction, so that the direction of maximum contrast of said liquid crystal layers lies between the 4:30 and 7:30 directions.

2. A liquid crystal display device as claimed in claim 1 in which one of the electrode substrates in contact with both liquid crystal layers.

3. A liquid crystal display device as claimed in claim 1 or 2 in which the liquid crystal layers are composed of the same liquid crystal material.

4. A liquid crystal display device as claimed in any preceding claim in which the long axes of the molecules of the liquid crystal layers are aligned in a given direction by rubbing the surfaces of the respective electrode substrates.

5. A liquid crystal display device substantially as herein described with reference to and as shown in the accompanying drawings.

6. A twisted nernatic type liquid crystal display having two liquid crystal layers between which a transparent electrode substrate is provided and a 3 GB 2 032 640 A 3 pair of polarizing plates on the outsides of said liquid crystal layers, wherein the long axis of the liquid crystal molecules in the lower part of the lower layer of said two liquid crystal layers is in the 9 o'clock to 3 o'clock direction, the long axis of the liquid crystal molecules in the upper part of the lower layer is in the 6 o'clock to 12 o'clock direction, the long axis of the liquid crystal molecules in the lower part of the upper layer is in 45 the 12 o'clock to 6 o'clock direction, the long axis of the liquid crystal molecules in the upper part of the upper layer is in the 9 o'clock to 3 o'clock direction from which the best contrast can be obtained in said upper and lower layers is in the four-thirty to seven-thirty direction.

7. A twisted nematic type liqud-crystai--displaydevice having two liquid crystal layers between which a transparent electrode substrate is provided and a pair of polarizing plates on the outsides of said liquid crystal layers, wherein the long axis of the liquid crystal molecules in the lower part of the lower layer of said two liquid crystal layers is in the 12 o'clock to 6 o'clock direction, the long axis of the liquid crystal molecules in the upper part of the lower layer is in the 9 o'clock to 3 o'clock direction, the long axis of the liquid crystal molecules in the lower part of the upper!ayer is in the 9 o'clock to 3 o'clock direction, th ' e long axis of the liquid crystal 65 molecules in the upper part of the upper layer is in the 6 o'clock to 12 o'clock direction, and the directions from which the best contrast can be obtained in said upper and lower layers is the four thirty and seven-thirty directions respectively. 70

8. A twisted nematic type liquid crystal display device having two liquid crystal layers between which a transparent electrode substrate is provided and a pair of polarizing plates on the outsides of said liquid crystal layers, wherein the long axis of the liquid crystal molecules in the lower part of the lower layer of said two liquid crystal layers is in the 12 o'clock to 6 o'clock direction, the long axis of the liquid crystal molecules in the upper part of the lower layer is in the 3 o'clock to 9 o'clock direction, the long axis of the liquid crystal molecules in the lower part of the upper layer is in the 3 o'clock to 9 o'clock direction, the long axis of the liquid crystal molecules in the upper part of the upper layer is in the 6 o'clock to 12 o'clock direction, and the directions from which the best contrast can be obtained in said upper and lower layers is the fourthirty and seven-thirtY direc.tions respectively.

9. A twisted nematic type liquid crystal display device having two liquid crystal layers between which a transparent electrode substrate is provided and a pair of polarizing plates on the outsides of said liquid crystal layers, wherein the long axis of the liquid crystal molecules in the lower part of the lower layer of said two liquid crystal layers is in the 3 o'clock to 9 o'clock direction, the. long axis of the liquid crystal molecules in the upper part of the lower layer is in the 6 o'clock to 12 o'clock direction, the long axis of the liquid crystal molecules irl the lower part of the upper layer is in the 12 o'clock to 6 o'clock direction, the long axis of the liquid crystal molecules in the upper part of the upper layer is in the 3 o'clock to 9 o'clock direction, and the direction from which the best contrast can be obtained in said upper and lower layers is in the four-thirty to seven-thirty direction.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.